1. Field of the Invention
The invention is directed to X-ray fluorescence systems and methods. More particularly, the invention is directed to microscopic X-ray fluorescence with focused X-ray beams.
2. Background Information
Most, if not all atomic elements will fluoresce when illuminated with X-ray energy. The resulting fluorescence spectrum is generally characteristic of the element. In the microelectronics manufacturing field, X-ray fluorescence is used to determine both the presence of elements and with appropriate conditions, the concentration of different elements in deposited layers. Under appropriate conditions, it is also possible to determine layer depths in microelectronics devices using X-ray fluorescence.
Quantitative analysis of the resulting X-ray fluorescence is frequently performed with a technique called fundamental parameters. Typically, analysis of X-ray fluorescence by the fundamental parameters technique uses the spectrum of fluorescence wavelengths and the relative intensities in that spectrum.
Given the analytic capabilities of X-ray fluorescence, and the decreasing size of features on microelectronics devices, microscopic X-ray fluorescence techniques were developed. However, in contrast to optical methods, X-rays are not easily susceptible to the known techniques of optical refraction using a lens. Thus, for applications where a low level of X-ray energy in a small or focused area is sufficient, systems use a high-power X-ray source and a pin-hole or very small aperture to provide X-ray illumination of the small area. However, this is inefficient and does not allow higher X-ray energy without significant and impractical increases in X-ray power. Therefore, techniques to focus X-rays are advantageous and have been developed. One such technique is the capillary optics technique. However, capillary optics for X-ray systems are known to produce a halo effect. Systems to eliminate or reduce the halo effect of an X-ray focusing system are needed.
The known microscopic X-ray fluorescence systems are less sensitive to low atomic number elements and are unable to detect elements below certain numbers. Systems and methods to detect lower atomic number elements are needed.
As the feature size on microelectronic devices decreases and focused X-ray systems generate smaller X-ray spots, it becomes hard to accurately locate particular features on a sample and then accurately position the focused X-ray spot on that particular feature. Systems and methods to accurately and reliably locate small features and position an X-ray spot on the feature are needed.
When X-ray fluorescence systems translate microelectronics wafers during the testing, it is possible that as a result of irregularities, the sample is not uniform or is improperly mounted and the sample contacts parts of the system. These collisions frequently destroy the sample and may damage or destroy parts of the system. Systems and methods to avoid contact between sample and system are needed.
The invention is directed to methods and systems of X-ray fluorescence, which are used to measure film thickness and perform analysis on the material composition of microelectronics. In one aspect, the invention provides an X-ray fluorescence system comprising an X-ray source; an X-ray focusing element with an input and an output end, the input end in proximity to the X-ray source; and an aperture disposed on the output end of the focusing element so as to substantially block unfocused X-rays, while allowing substantially complete transmission of focused X-rays. An object and advantage of this aspect is reduction or elimination of a halo effect in focused X-ray optic systems.
In another aspect, the invention provides an X-ray fluorescence system comprising an X-ray source, the source arranged to direct X-rays substantially perpendicular to a sample in a testing position; an imaging device for imaging the sample in a viewing position; and an automatic translation device cooperating with the imaging device and the X-ray source to translate between the viewing position and the testing position. An object and advantage of this aspect is to provide accurate location and positioning of an X-ray spot on a particular feature of a sample.
In another aspect, the invention provides an X-ray fluorescence system comprising an X-ray focusing element with an input end and an output end; an aperture disposed on the output end of the focusing element; and a vacuum source connectable to the X-ray focusing element for evacuating the X-ray focusing element. The X-ray detector is also connectable to a vacuum source. The sample remains at atmospheric pressure. An object and advantage of this aspect is to provide a system to detect low atomic number elements at production rates.
In another aspect, the invention provides a method for detecting elements with low atomic numbers in an X-ray fluorescence system comprising: positioning a sample for X-ray illumination by the X-ray fluorescence system; evacuating an X-ray focusing element with a vacuum source; and illuminating the sample with X-rays focused by the X-ray focusing element while the sample remains at atmospheric pressure. The X-ray detector may also be evacuated. An object and advantage of this aspect is to provide a method to detect low atomic number elements, at production rates. Higher through-put is enhanced by eliminating the need to vacuum cycle the sample chamber.
The foregoing specific objects and advantages of the invention are illustrative of those which can be achieved by the present invention and are not intended to be exhaustive or limiting of the possible advantages that can be realized. Thus, the objects and advantages of this invention will be apparent from the description herein or can be learned from practicing the invention, both as embodied herein or as modified in view of any variations which may be apparent to those skilled in the art. Accordingly the present invention resides in the novel parts, constructions, arrangements, combinations and improvements herein shown and described.